1. Field of the Invention
This invention relates to a geared electric motor provided with a rotation sensor for detecting rotation of the output shaft, which is used for driving, for example a window glass of a power window apparatus, a sunroof lid of a sunroof apparatus of motor vehicles or so.
2. Description of the Prior Art
As a geared electric motor with a rotation sensor for detecting the rotation of the motor shaft, a motor has been known, which is provided with a magnet secured to the armature shaft to be rotated according to power supply and a signal generating element disposed around about the magnet as disclosed in U.S. Pat. No. 5, 245,258.
In the power window apparatus or the sunroof apparatus incorporated with the electric motor of this kind, if an obstruction is caught between the window glass and the sash or he sunroof lid and the frame while the window glass or the sunroof lid is traveling in the closing direction, the armature shaft of the electric motor loses in rotational speed and the number of rotation signals generated from the signal generating element is reduced remarkably. The obstruction is detected to be caught according to the reduction in number of rotations of the armature shaft by the control circuit of the apparatus, and the obstruction is released before long by actuating the armature shaft of the electric motor in the reverse direction and driving the window glass or the sunroof lid in the opening direction.
In the aforementioned electric motor with the rotation sensor, the movement of the window glass or the sunroof lid is detected on basis of the rotation of the armature shaft of the motor, however the window glass or the sunroof lid is not combined directly with the armature shaft of the motor, but is connected with the output shaft through reduction gears composed of a worm formed on the armature shaft and a worm wheel meshed with the worm, and a rubber-made damper housed in the worm wheel. Therefore, when the obstruction is caught by the window glass or the sunroof lid, the reduction of the traveling speed of the window glass or the sunroof lid caused by the obstruction is transmitted to the armature shaft through the reduction gears including the rubber-made damper after plastic deformation of the damper and the reduction in the number of rotations of the armature shaft becomes smaller at the beginning of pinching of the obstruction. Accordingly, it takes a time for detecting the obstruction to be caught by the window glass or the sunroof lid and there is a problem in that there is the possibility of causing a time lag in the control for driving the window glass or the sunroof lid in the reverse direction.
This invention is made in view of the aforementioned problems of the prior art, and it is an object to provide a geared electric motor having a rotation sensor which is possible to improve the accuracy in detection of the rotation of the output shaft in the electric motor.
The geared electric motor according to this invention is characterized by comprising an armature shaft to be rotated according to introduction of electric current, reduction gears connected with the armature shaft for reducing rotational speed of the armature shaft, a damper combined with a final section of the reduction gears, an output shaft combined with load and the damper, speed increasing gears connected with the output shaft, a rotor connected with a final section of the speed increasing gears, and a rotation sensor for generating a signal according to rotation of the rotor.
In the geared electric motor according to this invention, the rotation of the armature shaft is given to the output shaft through the damper after reducing the rotational speed of the armature shaft by the reduction gears. The rotation sensor generates signals (rotation signal) in response to the rotation of the rotor which is rotated in the speed increasingly transmitted from the output shaft through the speed increasing gears. Accordingly, the rotation signal is generated accurately by the rotation sensor according to the rotation of the output shaft of the motor without influence of the plastic deformation of the damper and the scattering in the magnetizing.